I have just installed webers on my Cosworth with reindexed sprockets, it starts and runs but I get popping comming from intakes and some backfiring also, it seem to be very lean (pulled plugs and they are very clean white), I tried to adjust the mixture out but the popping is still around especially when choke is off and engine warmed)..

Does it usually need different jets with the reindexed sprockets, from what I read it makes for a leaner running engine to begin with,